IL-17A and IL-17F bind and activate IL-17RA. IL-17RA has been shown to be important in regulating immune responses. Activation of the IL-17RA leads to production of cytokines, chemokines, growth factors, and other proteins that contribute to the symptoms and/or pathology of numerous diseases. IL-17A is an inflammatory cytokine that induces the production of cytokines and other mediators leading to diseases and physiological effects such as inflammation, cartilage degradation, and bone resorption. IL-17A also plays a role in a number of inflammatory conditions including arthritis (rheumatoid arthritis), psoriasis, inflammatory bowel disease, multiple sclerosis, and asthma. (Li et al., 2004, Huazhong Univ. Sci. Technolog. Med. Sci. 24:294-296; Fujino et al., 2003, Gut. 52:65-70; Kauffman et al., 2004, J. Invest. Dermatol. 123:1037-1044; Mannon et al., 2004, N. Engl. J Med. 351:2069-2079; Matusevicius et al., 1999, Mult Scler 5, 101-104; Linden et al., Eur Respir J. 2000 May; 15(5):973-7; Molet et al., 2001, J. Allergy Clin. Immunol. 108:430-438). Recent studies have suggested that IL-17F plays a role in the induction of inflammatory responses (Oda et al., 2006, American J. Resp. Crit. Care Medicine, Jan. 15, 2006; Numasaki et al., 2004, Immunol Lett. 95:97-104).
Aspects of the invention provide for the identification of neutralizing determinants on IL-17RA that neutralizing antibodies bind and thereby inhibit IL-17 ligand family members from binding to and activating IL-17 Receptor A or a receptor complex comprising IL-17 Receptor A. Aspects of the invention also include antibodies that compete for binding with the IL-17RA neutralizing antibodies described herein.